<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
  <style>
    .fu {
      width: 500px;
      background-color: rgba(255,255,0,.6);
      overflow: hidden;
    }
    .fu>div {
      width: 100px;
      height: 100px;
      border: 2px solid #00f;
    }
    .d1 {
      background-color: red;
      /*float: right;*/
      float: left;
    }
    .d2 {
      background-color: green;
      /*float: right;*/
      float: left;
    }
    .d3 {
      background-color: blue;
      /*float: right;*/
        float: left;
    }
  </style>
</head>
<body>
  <div class="fu">
    <div class="d1"></div>
    <div class="d2"></div>
    <div class="d3"></div>
  </div>
</body>
</html>